996 DISEASES OF THE HOCK. 



The causa externa is almost exclusively represented by mechanical 

 injury. Severe, rapid work, especially under the saddle, or in front 

 of heavy loads, often produces slight, frequently repeated strain. 

 Peters thinks soft ground and rough pavements particularly injurious, 

 because the unavoidable rotary movement of the hoof on the ground 

 is interfered with, and consequently takes place, not at the extremity 

 of the limb, but in the joints, especially in the hock -joint. 



Single violent sprains, produced, for example, by wheeling round 

 on the hind-quarters or suddenly throwing the horse on its haunches, 

 may determine inflammation of the hock-joint, but this is far from 

 common. Even less frequently is inflammation caused by external 

 injuries, such as wounds or bruises. 



Frick, who lived for a long time in the mountainous parts of 

 Schleswig states that, with the exception of being rather kk leggy," 

 the horses there are well shaped. Nevertheless it very often happened 

 that when worked the animals developed acute lameness, with 

 swelling, heat, and pain on the inner side of the hock-joint. The 

 lameness was similar to that of well-marked spavin. Cold local 

 affusions and rest removed the symptoms in three to four days, but 

 very soon after, enlargement of the inner side of the hock and lameness 

 reappeared and the existence of lt spavin " could no longer be over- 

 looked. 



Frick, therefore, regards strains as playing the chief part in the 

 causation of spavin. The formation and function of the hock naturally 

 favour injuries of the kind, and Frick, after careful study, is convinced 

 of the truth of this view. As in every other form of strain, the 

 anatomical lesions may vary, and it is this variation in clinical 

 appearances which has caused different observers to formulate such 

 widely differing views as to the exact nature of spavin. 



Although agreement has not been reached as to the initial lesion 

 of spavin, the views regarding its pathololgy are more in accord. 

 Anatomy and physiology here play the chief part. The peculiar 

 fact that the disease affects the inner side of the hock has always 

 attracted attention, and has given rise to much speculation. 



Peters sought an explanation in the anatomical formation of the 

 parts. As the connection between the tibia and astragalus consists 

 of a ginglymoid, or, more correctly speaking, a screw-like, joint, in 

 which the powerful lateral ligaments limit both abduction and 

 adduction, and only allow of movement in the direction of the longi- 

 tudinal axis of the body, one would expect that the axis of the joint 

 would be perpendicular to that of the body. This is not the case, 

 however ; the (horizontal) axis of the joint lies obliquely to it, and, 



